Process and apparatus for working metals under high fluid pressure



Dec- 24, 1968 A. BOBROWSKY 3,417,539

PROCESS AND APPARATUS FOR WORKING METALS UNDER HIGH FLUID PRESSURE Filed Oct. 18, 1965 2 Sheets-Sheet l HG! A8 7 '9 .f I 7 1 22 "III //////////4 lo 2? I2:

46 'INVENTOR ALFRED BoaRowsKY Dec. 24, 1968 PROCESS AND APPARATUS UNDER HIGH FLU Filed Oct. 18. 1965 A. BOBROWSK FOR ID P KING METALS SURE 2 Sheets-Sheet 2 (III/[II INVENTOR ALFRED BOBROWSKY BY ATTOR Y United States Patent 3,417,589 PROCESS AND APPARATUS FOR WORKING METALS UNDER HIGH FLUID PRESSURE Alfred Bobrowsky, Livingston, N.J., assignor to Pressure Technology Corporation of America, Woodbridge, N.J., a corporation of Delaware Filed Oct. 18, 1965, Ser. No. 497,324 7 Claims. (Cl. 7260) ABSTRACT OF THE DISCLOSURE Method and apparatus for strawing and rafling at the highest pressure short of pinch off, in a pressure box having substantially landless seals at the entry end and exit end and each of said seal means being non-self-energizing.

This invention relates to a process and apparatus for working metals under high fluid pressure.

It is known that wire, rod, tubing, and profiled shapes can be made by passing metal through a die. If the die is round, wire and rod reduced in cross-section emerge from the die with a round cross-section. If the die has a profiled shape, the wire and rod emerge with the profiled shape. Either round or profiled wire and rod may be passed through either a round or a profiled die. Hollow tubing, whether round or of profiled shape, may be reduced in outer diameter by passage through a die, the process being termed sinking. A floating mandrel inside the hollow tubing additionally may be employed to size the inside diameter for long lengths of tubing. In the present invention, the term wire is meant to include wire, rod, tubing and profiled shapes.

If wire is pulled through a die, the process is termed wire-drawing, whereas if the wire is ejected from the die by the push of a solid ram, the process is termed forward or direct ram extrusion. If the die is pushed into a billet so as to eject wire, the process is termed backward or indirect ram extrusion.

When fluid pressure alone forces metal, initially contained in a pressure chamber, through a die into the atmosphere, the process is termed fluid extrusion or hydrostatic extrusion. In this latter process, the entire billet must be contained in the pressurized extrusion chamber, except possibly for an initially reduced portion passed through the die.

When fluid pressure alone forces metal through a die into a region at a lower fluid pressure, the process is termed fluid-to-fluid extrusion or differential extrusion. In this process also, the billet must be contained in a pressurized extrusion chamber or chambers.

When wire is drawn through a die with fluid pressure on both sides of the die, the process is termed wiredrawing under pressure. In this process, the Wire is initially in a pressure chamber or chambers.

When fluid pressure forces wire through a die while simultaneously the wire is pulled through the die, the process is termed combined fluid extrusion and wire drawing and, in this process also, the entire billet must be contained in a pressurized extrusion chamber or chambers.

When a wire is pulled through a die while simultaneously a lesser force pulls backward on the wire, the process is termed wire drawing with back pull or back tension.

The present invention, in one aspect thereof, relates to the drawing of wire through a die with fluid pressure on one side of the die only, the billet not being contained entirely in a pressure chamber but entering the latter through a pressure seal which permits wire to be drawn into the pressure chamber without escape of pressurized liquid from the chamber. This process is termed strawing. In this strawing process, the volume of the pressure chamber imposes no limitations on the initial length of the billet. Several advantages result from the use of the strawing process, for example the pressure chamber can be of a small size large enough for only two seals, one of which is a die, and a short length of billet therebetween.

A modification of the strawing process is termed raffing. In the rafting process, a drawing die is positioned in a pressure chamber with pressure on both sides of the die, the die being located between a seal at one end of the pressure chamber, through which the billet enters the chamber, and a seal at the other end of the pressure chamber through which the drawn wire leaves the pres sure chamber.

The pressure chambers employed in the present invention do not employ a fixed end wall. Advantages resulting from the use of a chamber with no fixed end wall are described in copending application Ser. No. 427,909, filed Jan. 25, 1965; for example, undesirable stress concentrations associated with a fixed end wall are eliminated.

For some time, a phenomenon known as the pinchingoff eflect has been known and this effect is described in the paper Breaking Tests Under Hydrostatic Pressure and Conditions of Rupture, by P. W. Bridgman, Philosophical Magazine (6), 24, 1912, p. 66. In a demonstration of the pinching-off effect, a straight rod of constant diameter is passed through a seal into a pressure chamber and out through another seal while pressure is applied to the chamber. Despite the fact that no pull is applied to the ends of the rod, the rod fails by tearing in two inside the chamber and the broken pieces are ejected, one from each end thereof. The pressure required to cause rupture of the metal rod ranges from a value about equal to the tensile strength of the material of the rod up to a value about 50% above the tensile strength.

Obviously, the pinching-off effect limits the maximum pressure that may be applied in a pressure chamber, through which a wire passes, to a value at most about 50% above the tensile strength of the wire. It was heretofore believed that the pinching-oft effect would limit the maximum pressure and also might cause tensile failure of the wire being drawn in a strawing or rafting process. Where the billet is completely contained within a pressurized chamber during extrusion, the pinching-off effect cannot occur. Similarly, where equal pressure exists on both sides of the die, the pinching-off effect cannot occur. Bridgman states on page 68 that the pinching-off effect can be dangerous and, on one occasion, a specimen 74, inch in diameter and 3 inches long penetrated 5 inches of wood when pinching-off occurred at a pressure of about 90,000 psi.

In the present invention, the pinching-off effect is automatically eliminated as a potential danger.

The invention will be further illustrated by reference to the accompanying drawings in which:

FIGURE 1 is a sectional view of one embodiment of an apparatus for conducting the strawing process of the present invention,

FIGURE 2 is a sectional view of one embodiment of an apparatus for conducting the rafling process of the present invention,

FIGURE 3 is a fragmentary sectional view of an apparatus for performing a co-strawing or cladding operation by strawing,

FIGURE 4 is a sectional view of one embodiment of an apparatus for cladding by strawing where the sheathing material is fed into the pressure chamber by fluid-to-fluid extrusion,

FIGURE 5 is a sectional view of one embodiment of an apparatus for use in a strawing process where the billet is heated while being strawed,

FIGURE 6 is a sectional view of one embodiment of a landless die for use in the strawing and rattling processes of the present invention, and

FIGURE 7 is a fragmentary, sectional view of an apparatus utilizing rollers instead of a die to effect deformation.

Referring to FIGURE 1, a solid metal block 2 has a pressure chamber 4 therein through which passes the billet and wire 6, 7, and 8. In the pressure chamber are mounted a combination die and exit seal and an entry seal 12. The diameter of the billet 6- entering the pressure chamber 4 is slightly larger than the throat of the entry seal 12, a suitable difference in diameter of a billet 0.125 inch in diameter being 0.005 inch, if the billet diameter does not depart greatly from its nominal diameter, but is not restricted to this value. If the difference is too small, surface imperfections in the billet will permit leakage of pressurized fluid from the chamber 4. If the difference is too large, the entry seal must work the billet material which is an inefiicient process. A difference of 0.00005 inch has been found to be too small and a difference of 0.012 inch has been found to be too large when the material being strawed or raifed is commercial quality annealed copper.

Large reductions can be obtained by strawing or railing so that reductions of and more in crosssectional area have been accomplished with both annealed and Worked copper in a single pass through a die, such as the die 10 of FIGURE 1, so that the cross-sectional area of the wire 8 is 50% or less than that of the billet 6.

Because of the pinching-off effect, the wire 7 between the seals 10 and 12 is under tension when the chamber 4 is pressurized. Pinching-olf will not occur when the strawing or rafliing process is properly performed.

The pressure chamber 4 is surrounded by an external casing 14 which restrains the seals 10 and 12 from expulsion from the chamber 4 when the latter is pressurized.

Pressurized liquid 16 is introduced into the chamber 4 through the bore 18 in the tube 19 which latter is reinforced by the sleeve 20. A jam nut 22 forces the tube 19 against a conical seat 24 in the metal block 2 to effect an initial seal. When pressure is applied in the bore 18, the conical tip of the tube 19 is further forced by the pressure against the conical seat in the block 2 thereby preventing leakage. Pressurized liquid passes through the bore 26 into the pressure chamber 4. The thrust of the liquid pressure downwardly on the chamber 4 is withstood by the base 28. Pressure is supplied by either a pump or an intensifier usually up to pressures of 500,- 000 p.s.i.

The outer surfaces of the seals 10 and 12 are secured against leakage by the O-rings 30 and 32. Such O-rings are adequate as static seals at pressures up to at least 600,000 p.s.i.

In operation, a pull is applied to the wire 8, previously reduced so as to pass through the seal 12 with a small interference (for example, 0.002 inch for a wire of 0.125 inch diameter) sufiicient to seal the pressure and to exceed variations in nominal diameter of the wire. The chamber 4 is pressurized, pull is increased, and the wire passes through the die 10 and is reduced, and shaped if the die is profiled. If an extremely low pressure is employed, for example 100 psi, a spacer 34 is required to prevent excessive movement of the seal 12. In usual practice, the fluid pressure force on the seal 12 is far greater than the force exerted by the billet 6 moving through the seal 12 so that no spacer is required. If a spacer is employed, it is slotted, drilled, or otherwise configured to permit passage of pressurized liquid therethrough.

The pressure is increased slowly, for example at the rate of psi. per second and, when a sufficiently high pressure is attained, the pinching-off tendency of the pressure causes the wire 7 to elongate and neck slightly in a seal. A minute leak occurs, venting pressurized liquid and thereby lowering the pressure to a suitable value in the pressure chamber 4 and the leak disappears.

Referring to FIGURE 2, an apparatus for performing the raffing process is shown in which a metal block 2 has a pressure chamber 4 therein, as in the strawing process of FIGURE 1. Pressurized liquid 16 is introduced through the bore 26 and passes through an aligned bore in the spacer 36. The billet and wire 6, 7, and 8 passes through an entry seal 12 of the type employed in the apparatus of FIGURE 1, and then passes through the throat of a die 38, having pressure on both sides thereof, after which the wire passes out of the apparatus through the exit seal 40. In this apparatus, the wire is worked by the die 38, having pressure on both sides thereof, which is positioned between the entry and exit seals 12 and 40, respectively. Very little work is perfromed on the wire 8 by the exit seal 40, the latter acting merely as a seal for the pressurized liquid. The seals 12 and 40 are sealed against leakage around the exteriors thereof by the O-rings 30 and 32, similarly to the construction of FIGURE 1. Also, as in the construction of FIGURE 1, the seals 12 and 40 are retained in the pressure chamher by the exterior casing 14.

The construction of the present invention permits the pressure in the pressure chamber to be as high as possible without rupture of the wire. This is accomplished by the use of the seals 10 and 12 in the strawing process and 40 and 12 in the raffing process. A usual type of seal for use in high pressure technology is a so-called self-energizing seal which has advantages for most applications in that the sealing pressure exceeds the pressure of fluid to be sealed so that no leakage can occur, and the seal contains a compressible member which is usually an elastomer, a polymer, or a hollow metal, which can expand and contract and so follow variations in diameter of the metal being drawn through the seal. Common seals of the self-energizing type are the unsupported area seal, the O-ring seal, and the U-section seal. These seals have the common characteristic that the sealing material presses against the Wire with a pressure exceeding that of the liquid being sealed. In each case, the intensification of pressure in the sealing process tends to cause pinch-off or necking of the wire under the compressible seal material. Thus, the pressure not only cannot rise above the value of the pinch-off pressure using such seals, it must remain well below it by a factor given by the ratio of sealing pressure to fluid pressure. The tendency of this type of seal to cause pinch-off is well known.

The seals used in the strawing and rafiing processes of the present invention are not of the self-energizing type but, instead, are of the types shown in FIGURES 1 and 2 of the drawings. When seals of the type shown are employed in either the strawing or rafting process and the pressure of the liquid in the pressure chamber rises above the pinch-off level, the wire tends to neck slightly in the seals thus providing a small clearance between wire and seal through which a minute amount of high pressure liquid escapes, thus lowering the pressure slightly below the region of the pinch-off effect. It is, therefore, possible to perform strawing and rafiing at the highest pressure short of pinch-off. In general, this maximum pressure increases as the wire is reduced since the wire increases in strength with the amount of working, thus permitting increased pressure without pinch-off.

Those processes which employ a billet contained in a sealed pressure chamber are totally inadequate when it is desired to fabricate a single length of wire under pressure. For example, one cannot readily fabricate a continuous ten-mile length of steel wire 0.10 inch in diameter in this manner, which wire is required for towing some supersonic aircraft targets, since an enormous pressure chamber would be required to contain the necessary amount of billet metal. In contrast to such processes, either strawing or raffiing permits the fabrication, under pressure, of continuous lengths greater than this. Thus, the present invention provides a means for fabricating very long or continuous lengths of wire.

A fluid may be employed in the pressure chamber 4 which is different from the fluid 16 employed to pressurize the chamber. Instead of a liquid, a paste, soft deformable solid, flowable solid, or other pressure-transmitting medium may be employed as long as it flows more readily than the wire. Accordingly, the present invention provides a process whereby a material may be selected for optimum lubrication of the wire during strawing or rafling and another material 16 may be selected that is optimum for generation of pressure and lubrication of the moving parts of the pressure generating system. For example, in the strawing of tough-pitch copper under pressures of 25,000 to 60,000 p.s.i., it has been found beneficial to employ as a pressure fluid in the pressure chamber a commercial drawing compound which is a paste, i.e., Oakite Special Drawing Compound, whereas the pressure fiuid 16 is an S.A.E. W mineral oil.

Some of the pressure fluid is carried through the seals 10 and 40 in FIGURES 1 and 2, respectively, during the strawing and rafling operations, presumably due to irregularities in the surf-ace finish of the wire. A typical thickness of fluid film carried through a seal of the non-selfenergizing type is about 5 microns or about 0.0002 inch. With an initial volume of about 0.4 cubic inch of fluid, it will be seen that about 20,000 inches (1667 feet) of wire 0.032 inch in diameter can be strawed before replenishment of the pressure fluid in the chamber 4 is required. Larger quantities of fluid, if required, can be easily supplied from a reservoir leading into the supply tube in both the strawing and rafting processes.

It has been found that lubrication under pressure during metal working reduces frictional forces, i.e., the higher the pressure the more effective the lubrication. The strawing and rafling processes of the present invention have, as a feature thereof, that lubricant is supplied to the die under high pressure, thus providing excellent lubrication. It also has been found that, under suitable conditions, the wire is completely separated from the metal of the die by a film of lubricant. Since die wear is thus minimized, long lengths of wire may be drawn without the diameter of the wire exceeding given tolerances, thereby eliminating interruption of the process to change dies and possibly limiting the length of continuously drawable wire.

The process of the present invention provides a high stress in the wire 8 of FIGURES 1 and 2. The additional lateral force supplied by the die to reduce the wire in cross-section is maintained at a low value, in turn reducing frictional force in the die to a minimum. This reduction in frictional force enables larger reductions to be made in a single strawing or rafiing pass through the die than if the stress in the wire were not present. For example, an annealed tough-pitch copper billet 0.125 inch in diameter was successfully strawed to yield a wire of 0.087 inch in diameter in a single pass, constituting a 50% reduction in area, under a pressure of 25,000 p.s.i. While the pressure was being reduced to 1,000 p.s.i., the billet continued to be pulled at the same rate through the apparatus of FIGURE 1 and the pulling wire broke, thus indicating that frictional forces in the die 10 had greatly increased when the pressure was reduced. Furthermore, the lowered lateral forces on the die reduce die wear and permit an improved film of lubricant to be present.

An additional feature of the process of the present invention is that it is possible to provide automatic maintenance of the pressure at an optimum level. Where a portion of a partially cold-worked billet has been annealed so that different parts of the length of the billet are of different strengths, it is possible to provide a constant small volumetric feed of pressurizing liquid 16 that automatically vents from the seals. When the weaker portion of wire reaches the seal, liquid pressure drops through venting and when the stronger portion of the billet reappears, pressure again builds up to an optimum value.

The present invention is not limited to the strawing and rafling of single-composition materials but also may be applied to the co-strawing of one material inside another, for example platinum over molybdenum. Strawing and raffing also are applicable to the fabrication of other plural-composition materials, for example spiralled wire inside ceramic insulation, in turn inside a stainless steel sheath.

As shown in FIGURE 3, cladding by strawing may be performed much as by fiuid extrusion. A hollow billet of aluminum 42 has a bore 44 therein through which passes a copper billet 46; the copper billet and aluminum are emitted as a clad wire 48 from the die 50. The billet of aluminum is contained entirely within the pressure chamber and, even though the aluminum billet is larger than the entrance to the die 50, it will be drawn into the die. Further, composite materials composed of fibers, particles, platelets, and other small inclusions may be placed in billets of metal, and strawing performed.

Another example of cladding by strawing is shown in FIGURE 4 where cable sheathing is shown as cladding by strawing. It is well known in the art of cable sheathing by lead, and especially by aluminum over copper, that the sheathing material must be heated to a relatively narrow range of temperature to perform successful sheathing. The process of FIGURE 4 is performed at/ or near room temperature. Lead or pure aluminum 52 is fed by fluid extrusion into the pressure chamber in the block 2 by means of high pressure liquid 16 introduced through the bore 54. A supply of high pressure lubricant 56 for the sheathing material is fed separately directly to the pressure chamber through the bore 58. A copper billet 60 is pulled into the chamber through the seal 12. The combined frictional pull of the copper and pressure of the liquid on the sheathing material results in a sheathed cable 62 being formed by passage through the die 64. A major advantage of this process is that there is no friction of the sheathing material 52 on the wall 66 of the fluid extrusion chamber, thus permitting very large quantities of sheathing material to be clad without interruption of the process. This is an advantage since it is well known that flaws in sheathing can result when the conventional hot sheathing process is interrupted to add another batch of sheathing material.

Nominally brittle materials can be raffed provided the materials become ductile under pressure in the pressure chamber. Since brittle materials might fracture in entering the pressure chamber through a relatively non-conforming seal, the seal, when drawing such brittle materials, can be encased by a thin layer of low-friction conformable material, such as polytetrafluoroethylene, so that small variations in diameter of the entering billet can be tolerated without fracture of the billet.

Some materials, such as tungsten, do not become adequately ductile under lower pressures. In order to conduct commercially suitable strawing, the pressure at which ductrlity is obtained can be lowered by heating the billet to be strawed. For tungsten, 900 F. is a suitable temperature since it is ductile at atmospheric pressure at 900 F., whereas tungsten remains brittle at pressures up to 140,000 p.s.i., at room temperature. A tungsten billet can be resistance-heated by passing electric current through it by means of the conducting shoes 68 shown in FIG- URE 5. Cooling coils 70 can be employed, if desired, to reduce the temperature of the pressure chamber. The seals are electrically insulated from the pressure chamber.

Another advantage of the strawing and rafiing processes is the elimination of yield drop because the presence of high pressure alone has been found to eliminate it. For example, 90,000 p.s.i. has been found to eliminate yield drops in iron and nickel.

All spacers between seals or between seals and dies are slotted, drilled, or otherwise configured so as to impose minimal resistance to the passage of high pressure liquid in both the strawing and rafimg processes. The greatly reduced die wear made possible by the combination of low lateral force on the die during strawing or rafting and lubrication under exceedingly high pressures makes possible the fabrication of extremely long lengths of wire of essentially constant diameter, as compared to current practice where shorter lengths must be fabricated because die wear is sufiiciently significant that the later lengths drawn are substantially larger in diameter than the initial lengths drawn.

Heat is generated in metal being deformed in metalworking or metal-forming processes for three major reasons: (a) alteration in shape due to reduction of crosssectional area of the billet being deformed, (b) change of angle as the billet enters the die and again when it leaves the die (redundant work), and (c) friction between the billet and the die.

The strawing and rafiing processes of the present invention generate less heat than others mentioned above because a major feature of the dies of the present invention is that they have a throat which contains zero length of land, and, thus, the die is termed a landless die. Such a landless die is shown in FIGURE 6. Usual dies for wire drawing and/or extrusion contain a throat of constant diameter for a portion of the length of the die. This is not true in the preferred dies for use in strawing and rafting.

The automatic-control feature of the strawing and raffing processes entails a slight necking of the wire being drawn at the throat of the die in order to permit a small amount of liquid to escape. The mechanism by which the landless die provides automatic control of pressure without breakage of the wire is that a minute neck appears at the minimum diameter of the die thus enabling the entire portion of wire entering the die to draw back slightly, permitting the escape of liquid through the conical portion of the die and through the slight vent formed by the neck. When a die has a land present, a neck may form within the length of the land but sealing of the liquid still will occur at the ends of the land. In order for a die with a land to permit venting of a liquid, the neck must be longer than the land. It has been established that necking of metal under tension is a local phenomenon and the process proceeds primarily by continual reduction of the diameter of the wire until rupture occurs without major alteration of the length of the neck once the latter begins to form. Thus, when a wire in a die having a land begins to neck, the neck will continue to diminish the diameter of the wire without leakage occurring if the land continues to seal the wire. Rupture will thus occur rather than venting of the liquid pressure. In practice, it has been found that the necking on a wire of 0.057 inch nominal diameter results in a reduced diameter no less than 0.0565 inch. Dies of slightly longer lands can be employed in some embodiments of the present invention but the use of landless dies is especially preferred.

In the event cooling is required, the entire pressure chamber can be surrounded by cooling coils carrying a continuously replenished supply of coolant. It is also possible to vent high pressure liquid, thus carrying off heat by mass transport. Further, it is possible to cool the billet before it enters the die. In general, the mass of billet in the pressure chamber is small compared to the surface area of the latter so that no cooling other than natural convection is required. Since little or no heating of the billet usually is required in the processes of the present invention, since pressure replaces temperature, the processes, in general, do not generate excessive heat.

Further, the die in the rafiiing process of FIGURE 2 may be replaced by rollers. Rolling is conventionally effected by driven rollers between which metal is reduced or by pulling metal through non-driven rollers, i.e., pull rolling. Pull rolling has been effected under pressure in a manner such that the billet to be rolled is in a closed pressure chamber. Such a device is shown in FIGURE 7, where rolls 38' held in hearing blocks 38" effect deformation of the workpiece 7.

In the present invention, the material to be rolled, whether in the form of a sheet, strip, round rod, profiled shape, composite metal, or hollow tube, enters and leaves the pressure chamber through seals of suitable shape of the non-self-energizing type, as in the strawing and rafting processes described above. It is thereby possible to obtain for rolling the advantages of strawing and rafling, such as high ductility of material to be worked under pressure at or near room temperature, reduction or elimination of intermediate anneals for multiple passes, minimum work required in the rollers due to pinch-off stressing, automatic control of pressure at the highest desirable levels as determined by the strength of the material to be Worked and already worked, and others.

The rollers may be either idler rollers or driven rollers. If driven, the driving means may be electric or hydraulic motors in the presure vessel, or the rollers may be driven by shafting or other driving means passing through the sealed wall of the pressure vessel. There is no restriction on the type of rolls employed but, in general, just as in non-pressure processes, small area of contact rollers are most desirable. For this reason, systems such as fourhigh, planetary, cluster, and others designated by names such as Sendzimir and Kocks are preferred but not necessary. Further, the exit seal can serve as a planishing die for mills, such as a cluster mill, that ordinarily emit metal with a slightly rippled surface. Here too, the large reduction in rolling force made possible by the pinch-off force is a major advantage as is the presence of lubricant under pressure.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the pre sent invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. An apparatus for working metals under high fluid pressures comprising: a pressure chamber; means for introducing a fluid into the chamber under high pressure; an entry seal means through which metal stock is introduced into the chamber and an exit seal means through which worked metal stock is withdrawn from the chamber; each of said seal means being of the non-self-energizing type, said second seal means being a landless seal presenting a smaller opening to the metal to be worked than the opening presented by said first seal means whereby metal is worked when it passes completely through said pressure chamber and a metal deforming means in said chamber.

2. An apparatus according to claim 1 in which the metal deforming means includes a die which is the exit seal means through which worked metal stock is withdrawn from the apparatus.

3. An apparatus according to claim 1 in which the metal deforming means is a die mounted in the chamber between the two seal means.

4. An apparatus according to claim 1 in which spacer means is mounted between the two seal means.

5. An apparatus according to claim 1 including means for heating the metal stock while in the chamber.

6. An apparatus according to claim 1 in which the References Cited UNITED STATES PATENTS 8/1894 Robertson 7260 5/1941 Fogg 72-268 Simons 72-268 Hurwitz 72-288 CHARLES W. LANHAM, Primary Examiner 5 K. C. DECKER, Assistant Examiner.

US. Cl. X.R. 

